Scalp recorded auditory evoked potentials and sonomotor responses: An evaluation of components and recording techniques

Abstract

Early (0–8 msec), middle (8–50 msec) and long (50–500 msec) latency auditory evoked potentials (AEPs) were recorded from the scalp, ear, nose and mastoid regions of normal adult subjects using a balanced sternovertebral non-cephalic reference system. This study intended to differentiate neurogenic from myogenic components. Components judged to be neurogenic were greatest in amplitude at frontocentral scalp recording locations and were recorded during sleep. Some of these potentials were also recorded from the ear, mastoid and nose which suggests that these locations are often not ideal reference sites for recording AEPs. Certain scalp recorded middle and long latency AEPs were characterized by progressive shifts in their peak latencies in the sagittal and coronal planes. This “traveling wave” phenomenon suggests that these potentials arise in multiple spacially fixed cerebral generators. Components judged to be myogenic had latencies of 8–60 msec, were widely distributed over the scalp and were of greatest amplitude in relationship to actively contracting scalp muscle groups. One of these potentials, the post-auricular response, was recorded from the ear, mastoid and postauricular region. Except for the post-auricular response, these potentials were not observed in sleeping subjects. This suggests that middle latency AEPs can be recorded free of evoked myogenic contamination in normal adults during sleep if the recording electrode is not placed in the vicinity of the ear.